diff --git a/app/Services/CleanupSubscriberIntegrationsService.php b/app/Services/CleanupSubscriberIntegrationsService.php
index c7ef115..ec8268a 100644
--- a/app/Services/CleanupSubscriberIntegrationsService.php
+++ b/app/Services/CleanupSubscriberIntegrationsService.php
@@ -104,8 +104,8 @@ final class CleanupSubscriberIntegrationsService
         }
 
         $subscriberUid = $search['subscriber_uid'];
-        $phoneEnabled = $page->isPhoneFieldEnabledForSubscribers();
-        $data = MailwizzSubscriberFormPayload::baseFields($subscriber, $config, $phoneEnabled);
+        /** @var array<string, mixed> $data */
+        $data = [];
 
         $couponField = $config->field_coupon_code;
         if (is_string($couponField) && $couponField !== '') {
@@ -123,6 +123,10 @@ final class CleanupSubscriberIntegrationsService
             $data[$tagField] = MailwizzCheckboxlistTags::removeValueFromCsv($existingCsv, $tagValue);
         }
 
+        if ($data === []) {
+            return;
+        }
+
         $service->updateSubscriber($listUid, $subscriberUid, $data);
     }
 
diff --git a/app/Services/MailwizzService.php b/app/Services/MailwizzService.php
index d35ea1d..51c2dab 100644
--- a/app/Services/MailwizzService.php
+++ b/app/Services/MailwizzService.php
@@ -202,7 +202,8 @@ final class MailwizzService
         $out = [];
         foreach ($data as $key => $value) {
             if (is_array($value)) {
-                $out[$key] = $value;
+                // Empty arrays are omitted by Laravel's multipart encoder (no KEY[] parts), so Mailwizz never clears checkboxlist fields.
+                $out[$key] = $value === [] ? '' : $value;
 
                 continue;
             }
diff --git a/tests/Feature/DestroySubscriberTest.php b/tests/Feature/DestroySubscriberTest.php
index 31afe22..938edbe 100644
--- a/tests/Feature/DestroySubscriberTest.php
+++ b/tests/Feature/DestroySubscriberTest.php
@@ -194,6 +194,68 @@ class DestroySubscriberTest extends TestCase
         Http::assertSentCount(3);
     }
 
+    public function test_delete_clears_mailwizz_checkboxlist_when_only_configured_tag_is_present(): void
+    {
+        Http::fake(function (Request $request) {
+            $url = $request->url();
+            if (str_contains($url, 'search-by-email')) {
+                return Http::response(['status' => 'success', 'data' => ['subscriber_uid' => 'sub-single-tag']]);
+            }
+            if ($request->method() === 'GET' && str_contains($url, '/subscribers/sub-single-tag') && ! str_contains($url, 'search-by-email')) {
+                return Http::response([
+                    'status' => 'success',
+                    'data' => [
+                        'record' => [
+                            'TAGS' => 'preregister-source',
+                            'COUPON' => 'PREREG-OLD',
+                        ],
+                    ],
+                ]);
+            }
+            if ($request->method() === 'PUT' && str_contains($url, '/subscribers/sub-single-tag')) {
+                $body = $request->body();
+                $this->assertStringContainsString('TAGS', $body);
+                $this->assertStringNotContainsString('preregister-source', $body);
+                $this->assertStringNotContainsString('TAGS[]', $body);
+                $this->assertStringContainsString('COUPON', $body);
+
+                return Http::response(['status' => 'success']);
+            }
+
+            return Http::response(['status' => 'error'], 500);
+        });
+
+        $user = User::factory()->create(['role' => 'user']);
+        $page = $this->makePageForDestroyTest($user);
+        MailwizzConfig::query()->create([
+            'preregistration_page_id' => $page->id,
+            'api_key' => 'fake-api-key',
+            'list_uid' => 'list-uid-1',
+            'list_name' => 'Main list',
+            'field_email' => 'EMAIL',
+            'field_first_name' => 'FNAME',
+            'field_last_name' => 'LNAME',
+            'field_phone' => null,
+            'field_coupon_code' => 'COUPON',
+            'tag_field' => 'TAGS',
+            'tag_value' => 'preregister-source',
+        ]);
+
+        $subscriber = Subscriber::query()->create([
+            'preregistration_page_id' => $page->id,
+            'first_name' => 'Solo',
+            'last_name' => 'Tag',
+            'email' => 'solo-tag@example.com',
+            'coupon_code' => 'PREREG-LOCAL',
+        ]);
+
+        $response = $this->actingAs($user)->delete(route('admin.pages.subscribers.destroy', [$page, $subscriber]));
+
+        $response->assertRedirect(route('admin.pages.subscribers.index', $page));
+        $this->assertDatabaseMissing('subscribers', ['id' => $subscriber->id]);
+        Http::assertSentCount(3);
+    }
+
     public function test_delete_removes_coupon_code_in_weeztix_when_configured(): void
     {
         Http::fake(function (Request $request) {